EP0197095B1

EP0197095B1 - Feeder device for pressure chamber grinder

Info

Publication number: EP0197095B1
Application number: EP85904976A
Authority: EP
Inventors: Jouko Niemi
Original assignee: Finnpulva Oy AB
Current assignee: Finnpulva Oy AB
Priority date: 1984-10-12
Filing date: 1985-10-11
Publication date: 1990-02-07
Also published as: US4720049A; DK275186A; NO862341L; NO163216B; DK275186D0; NO163216C; FI69255B; NO862341D0; WO1986002287A1; FI844028A0; DE3575876D1; DK155871B; DK155871C; JPS62500504A; FI69255C; JPH0378145B2; EP0197095A1; FI844028A

Abstract

Device for feeding a material to be ground into a pressure chamber grinder provided with an equalizing tank (1), in which said equalizing tank (1) there is substantially the same pressure as in the pre-grinding part of the grinder, with which said pre-grinding part the equalizing tank (1) communicates via screw conveyor. The said device is installed in the top portion of the equalizing tank. The device is characterized in that it comprises a substantially vertical, conical feeder chamber (4), whose volume is, at the maximum, about one quarter of the volume of the equalizing tank (1) and at whose top end there is a feed opening (2) and, at the bottom end, an exhaust opening (3) larger than the feed opening (2); valve members (5, 6) arranged in the said openings (2, 3) and having diameters corresponding to the said openings (2, 3, respectively), the said valve members (5, 6) being provided with elastic closing members, operating in the way of an annular muscle for closing and opening the said openings (2, 3); a gas feed pipe (8) passing into the top portion of the feeder chamber (4) and provided with a valve (7) for the generation of a pressure impact in the top end of the feeder chamber (4), and a gas-removing pipe (10) provided with a valve (9), for lowering the pressure prevailing in the feeder chamber.

Description

The present invention is concerned with a device for feeding a material to be ground into a pressure chamber grinder provided with an equalizing tank, in which said equalizing tank there is substantially the same pressure as in the pregrinding part of the grinder, with which said pre-grinding part the equalizing tank communicates via a screw conveyor, the said device being installed in the top portion of the equalizing tank, the device comprising a substantially vertical feeder chamber at whose top end there is a-feed opening and, at the bottom end, an exhaust opening; valve members arranged in the said openings; a gas feed pipe passing into the top portion of the feeder chamber and provided with a valve, for the generation of a pressure impact in the feeder chamber.
As a feeder device for pressure chamber grinders, usually a so-called plug feeder is used, by means of which the material to be ground is fed into the equalizing tank as a gas-tight plug, as is described, e.g., in the International Patent Publication No. W084/03455. The ejector feeder devices, which are commonly used in conventional jet grinder devices, are not at all suitable for being used in pressure chamber grinders, owing to the very high operating pressures in the latter. On the contrary, a plug feeder is excellently suitable for this purpose in the case that the properties of the material can be compressed into gas-gas tight plug. There are, however, also many such materials as would be otherwise well suitable for grinding in a pressure chamber grinder but as cannot be compressed into a gas-tight plug. Such materials are e.g., granular materials and kernels of grain.
From the document US-A-3 257 080 an apparatus for processing anisotropic solid substances is known. Said apparatus comprises a charge chamber for receiving the substance to be processed, which chamber is provided with an inlet and an outlet, means for introducing a fluid under pressure into the charge chamber to subject the substance therein to a predetermined input energy, a quick-opening valve in the outlet of the chamber for controlling confluent discharge of the substance and fluid from the charge chamber, a receiving chamber as well as conducting means between the charge chamber and the receiving chamber for conducting the substance and fluid from the discharge chamber to the receiving chamber when the quick-opening valve is opened. The charge chamber will be pressurized to a preselected pressure in order to reach a supersonic velocity in the conducting means when the quick-opening valve is opened. When entering the receiving chamber the substance fluid mixture will be subjected to an explosive force caused by the rapid expansion of pressure fluid as well as to any vibrations and shock waves which may occur. The separation process is batchwise giving considerable variations in the particle size of the final products, especially between the product received in the beginning of a batch and in the middle of a batch. Further the hopper-like bottom portion of the charge chamber will require a very high pressure difference between the charge chamber and the receiving chamber which cannot be used in a pressure chamber grinder equipment, where the pressure in the equalizing tank must continuously be kept at a substantially constant level. Further the previously known apparatus cannot at all be used if the pressure in the system after each batch is higher than the atmospheric pressure, because of counter blast through the charging port of the charge chamber. If there continuously would be a high pressure in the system valves of an ordinary type would be worn out and become unusable in a few hours.
The object of the present invention is to permit the grinding of materials which cannot be compressed into a gastight plug in a. pressure chamber grinder, in view of the good energy economy and excellent grinding properties of the said grinder. This can be accomplished by means of a device in accordance with the invention, which is characterized in that the feeder chamber is conical, having a volume at the maximum about one quarter of the volume of the equalizing tank; the exhaust opening being larger than the feed opening; the said valve members having diameters corresponding to the said openings and being provided with elastic closing members, operating in the way of an annular muscle for closing and opening the said openings, the pressure impact being generated in the top portion of the feeder chamber, and that a gas-removing pipe provided with a valve, for lowering the pressure prevailing in the feeder chamber, is connected to said feeder chamber. Other embodiments of the invention come out from the accompanying claims 2 to 7.
In the following, the present invention will be described in more detail with reference to the accompanying drawing, which illustrates an example of a device in accordance with the invention.
The feeder device concerned comprises a substantially vertical conical feeder chamber 4, which is installed in the top portion of the equalizing tank 1 of the pressure chamber grinder, which is provided with a feed opening 2 and an exhaust opening 3, and whose volume is at the maximum about a quarter of the volume of the equalizing tank 1. The diameter of the exhaust opening 3 is larger than that of the feed opening 2. At these openings 2, 3, valve members 5, 6 are mounted whose diameters correspond to the said openings 2 and 3, respectively, which said valve members are provided with elastic closing members operating in the way of an annular muscle, for the purpose of closing and opening the said openings 2, 3. A gas feed pipe 8 provided with a valve 7 is passed into the top portion of the feeder chamber 4 so as to generate a pressure impact. Also, a gas-removing pipe 10 provided with a valve 9 is passed from the top portion of the feeder chamber 4 so as to lower the pressure in the feeder chamber 4 to the pressure of the surrounding atmosphere.
A prerequisite for the possibility of using such a valve feeder device is that the pressure chamber grinder is provided with an equalizing tank 1, in which substantially the same pressure prevails as in the pre-grinding part of the grinder and in which the material to be ground is made loose, e.g., by means of a rotor before it is fed into the said pre-grinding part by means of a screw conveyor. In order that a good grinding result could be achieved, it is, viz., required that the material to be ground is fed as a very uniform flow into the pre-grinding chamber.
The feed opening 2 of the device is preferably provided with a feed funnel 11 for receiving the material to be ground, e.g., from the conveyor belt (not shown) or from a storage silo. In order to determine the batch of material fed, it is possible, e.g., to provide weighing devices underneath the equalizing tank 1, which indicate the quantity of material present in the equalizing tank. In addition to this, it is, e.g., possible to install weighing devices so as to detect the quantity of material present in the storage silo. In order to intensify the filling of the feeder chamber 4, a pushing piston 12 which operates vertically and which is placed in line with the feed opening of the device is favourably installed above the feed funnel 11, which said piston 12 is arranged so as to push and to compact the material to be ground into the feeder chamber 4. The use of a pushing piston 12 is advantageous in particular when the material to be ground has a very low bulk density. Since the weight of the material batch fed into the feeder chamber 4 can be increased thereby, the quantity of working gas required to detach the material and the number of times of actuation of the valves are reduced considerably per ton of material.
The filling of one batch of material into the equalizing tank 1 takes place as follows:
The exhaust valve 6 of the device and the valves 7, 9 of both of the gas pipes 8, 10 are kept closed; only the feed valve 5 of the device is kept open. The material to be ground is fed into the feed funnel 11 of the device, and it is allowed to flow from the feed funnel 11 into the feeder chamber 4 of the device. In order to intensify the filling, the pushing piston 12 of the device is preferably arranged so as to perform a few pushing strokes each time when a new batch of material has been transferred into the feed funnel 11. When the feeder chamber 4 is filled ready, the feed valve 5 is closed and the exhaust valve 6 is opened, whereupon the valve 7 in the gas-feed pipe 8 is opened so as to produce a pressure impact in the top portion of the feeder chamber 4. By the effect of the pressure impact, the batch of material present in the feeder chamber is detached and falls down into the equalizing tank 1. Owing to the conical shape of the feeder chamber 4, the transfer of the material into the equalizing tank 1 takes place immediately, because there are no choking portions between the feeder chamber 4 and the equalizing tank 1, but the flow channel formed by the feeder chamber 4 and by the exhaust valve 6 becomes substantially all the time wider when moving towards the equalizing tank 1. If the diameter of the exhaust valve 6 were equal to that of the feed valve 5, a choking portion similar to a bottle-neck would be formed in the bottom portion of the feeder chamber, which would hamper and, in the worst case, completely block the transfer of material into the equalizing tank 1, in particular if the material to be ground is readily clodding. After the feeder chamber 4 has been emptied, the exhaust valve 6 and the valve 7 of the gas-feed pipe 8 are closed and the valve 9 of the gas-removing pipe 10 is opened in order to lower the pressure prevailing in the feeder chamber 4 to the level of the pressure of the surrounding atmosphere, whereupon the valve 9 is closed and the feed valve 5 is opened in view of receiving a new batch of material.
As was already stated above, it is a prerequisite for the obtainment of a good grinding result that the feed of material by means of a screw conveyor into the pre-grinding chamber must be kept as uniform as possible. Moreover, a relatively constant gas pressure must be maintained in the pre-grinding chamber and also in the equalizing tank. By selecting the size of the feeder chamber 4 such that its volume is no more than about one quarter of the volume of the equalizing tank 1, it is made sure that the pressure impacts produced in the feeder chamber 4 do not have a significant effect on the pressure prevailing in the equalizing chamber.
In order that a wear-resistant feeder device reliable in operation could be provided, both the feed valve (5) and the exhaust valve (6) of the device must be of a type that has an elastic closing member operating in the way of an annular muscle. In such a valve, which is usually called a premaflex valve, no major wear occurs. On the contrary, a closing valve of an ordinary type would be worn out and become unusable in a few hours in a feeder device of this type.
The gas-feed pipe 8 is preferably connected to a gas source which has a gas colder than the working gas and whose pressure is about 0.5 bar higher than the pressure prevailing in the equalizing tank. Cold gas is fed into the feeder chamber 4 in order that the high temperature prevailing in the pressure chamber grinder should not be transferred into the feed funnel and into the storage silo, which said high temperature would have a detrimental effect on the entire feed process. By using a positive pressure of 0.5 bar, a sufficiently high pressure impact is produced, which does, however, not have a significant effect on the pressure prevailing in the equalizing tank. By connecting the gas-feed pipe 8 to the working-gas line of the pressure chamber grinder before the superheater, a gas of a suitable temperature and pressure is obtained.
If the pressure chamber grinder equipment includes a storage silo, the gas-removing pipe 10 can be connected advantageously to the bottom part of the silo, whereby the gas discharge taking place from the feeder chamber 4 at the end of each feeding step is utilized for loosening the material in the silo.
All the operations of the feeder device are preferably controlled by means of a programmed logic unit, which receives impulses from a sensor placed in the feeder chamber 4 and arranged so as to detect when the feeder chamber 4 is empty, from a sensor placed in the equalizing tank 1 at a predetermined height and arranged so as to detect the upper level of the material quantity present in the equalizing tank 1, which said level must not be higher than the said height, as well as from a sensor placed in the working-gas line of the pressure chamber grinder and arranged so as to detect when working gas is being passed into the pressure chamber grinder. Thereat it is preferable that the exhaust valve (6) and the feed valve (5) operate hydraulically or pneumatically. A new filling step starts when the feeder chamber 4 is empty, the quantity of material in the equalizing tank does not exceed the predetermined level, and working gas is being passed into the pressure- chamber grinder, i.e. the pressure chamber grinder is in operation.
To keep the friction between the material to be ground and the wall faces of the feeder chamber 4 as low as possible, the said wall face may be coated, e.g., with a special paint or with teflon, or be lined, e.g., with a noble-metal layer.

Claims

1. Device for feeding a material to be ground into a pressure chamber grinder provided with an equalizing tank (1), in which said equalizing tank (1) there is substantially the same pressure as in the pregrinding part of the grinder, with which said pre-grinding part the equalizing tank (1) communicates via a screw conveyor, the said device being installed in the top portion of the equalizing tank (1), the device comprising a substantially vertical feeder chamber (4) at whose top end there is a feed opening (2) and, at the bottom end, an exhaust opening (3); valve members (5, 6) arranged in the said openings (2,3 respectively); a gas feed pipe (8) passing into the top portion of the feeder chamber (4) and provided with a valve (7), for the generation of a pressure impact in the feeder chamber (4), characterized in thatthe feeder chamber (4) is conical, having a volume at the maximum about one quarter of the volume of the equalizing tank (1); the exhaust opening (3) being larger than the feed opening (2); the said valve members (5,6) having diameters corresponding to the said openings (2, 3 respectively) and being provided with elastic closing members, operating in the way of an annular muscle for closing and opening the said openings (2, 3); the pressure impact being generated in the top portion of the feeder chamber (4), and that a gas-removing pipe (10) provided with a valve (9), for lowering the pressure prevailing in the feeder chamber, is connected to said feeder chamber (4).

2. Device as claimed in claim 1, characterized in that the gas-feed pipe is connected to a gas source, which has a gas colder than the working gas and whose pressure is about 0.5 bar higher than the pressure prevailing in the equalizing tank (1).

3. Device as claimed in claim 2, characterized in that the face of the inside wall of the feeder chamber (4) has been treated in orderto reduce the friction.

4. Device as claimed in claim 3, characterized in that a feed funnel (11) is provided outside the feed opening (2), and a vertical pushing piston (12) is placed in line with the feed opening (2).

5. Device as claimed in claim 4, characterized in that the gas-feed pipe (8) is connected to the working-gas line of the pressure chamber grinder before the superheater.

6. Device as claimed in claim 5, characterized in that the exhaust valve (6) and the feed valve (5) operate hydraulically or pneumatically.

7. Device as claimed in any of the preceding claims, characterized in thatthe device operates as controlled by a programmed logic unit.